Coating composition comprising cellulose-aceto-propionate and an alkyd resin



Patented May 27, 1947 COATING COMPOSITION COMPRISINGCELLULOSE-ACETO-PROPIONATE AND AN ALKYD RESIN Harry K. Ash, Cincinnati,Ohio, assignor to Interchemical Corporation, New York, N. Y., a

corporation of Ohio No Drawing. Application July 1, 1943, Serial No.493,113

1 Claim. 1

This invention aims to provide a temporary protective coating for metaland similar impervious surfaces, characterized by the properties ofunusual strength and resistance to abrasion, coupled with the ability tostrip cleanly from a metal surface even after a prolonged period oftime.

In the metal working field, there has existed a considerable demand fora temporary protective coating which would serve to protect the metalagainst abrasion until the metal object is actually put into use, butwhich is easily removable from the metal surface thereafter. This demandhas existed with respect to decorative metal objects, where it isdesired to retain the metallic luster and sheen of a polished surfaceduring packing, shipping and handling prior to actual installation. orsale to a customer for use in the home. A more important use has been inthe commercial field. where it is desired to protect a portion of ametal surface from damage during machining or working of the rest of thesurface, or to protect an entire surface from surface marring while apiece of metal is bent, or otherwise deformed.

It has been proposed to use a wide variety of compositions for theproduction of temporarily adherent films. Transparent foils made fromCellophane, cellulose derivatives and resins have been suggested, butthe task of fitting preformed foils onto irregularly shaped objects hasmade this approach unsuccessful. Various coating compositions whichdeposit a film have likewise been tried. including rubber latex, andcellulose ester and ether lacquers. Many of the compositions require amultiple treatment of the surface to obtain the desired result; this ishighly undesirable from the cost standpoint. Other compositions are toosoft to withstand abrasion; others do not strip cleanly from themetallic surface. either because of adhesion, or because the films tearon attempted removal: and many others which strip for a few days losethe power to strip on ageing.

I have discovered a new type of coating composition which in oneapplication produces on metal a temporarily protective film which ischaracterized by high resistance to abrasion, and the ability to stripcleanly from the metal even after prolonged standing. My compositionsconsist essentially of solutions of cellulose aceto-propionate, insolvent combinations consisting of at least 75% active solvent for thecellulose ester, the compositions being further characterized by aminimum viscosity of 50 seconds in a No. 4 Ford cup at F.

According to my investigations, cellulose acetopropionate is uniqueamong the cellulose derivatives in that it yields films with the optimumcombination of film strength and strippability 2 from metal. Othercellulose derivatives either tend to adhere more to metal, or to yieldfilms of lower strength.

The cellulose aceto-propionate which I use may be of any of thecommercial grades available. These generally contain about 15.5% acetyland 31.5% propionyl content, and vary in viscosity from low to high. Thelow viscosity ester has a viscosity of 2 seconds, measured by the timerequired for a inch diameter steel ball to fall in a 1 inch tube througha 10 inch depth of a 2% solution in acetone at 25 C.; the high viscositymaterial has a 30 second viscosity. I prefer the low viscosity material,as it gives more concentrated solutions and thicker films; but the highviscosity product can be used.

Preferably, the aceto-propionate should be plasticlzed. Unplasticizedfilms will strip satisfactorily, but lack the versatility of plasticizedfilms. However, in order to keep the film sufficiently hard to withstandabrasion, the plastlcizer should preferably not exceed the weight of thecellulose ester.

Some resin may be used in the composition, so long as not so much resinis used that the film adheres too strongly to the surface coated. Theamount which may be used varies depending upon the resin used and theadhesion imparted to the film thereby. In general, the amount of resinand plasticizer present should not substantially exceed the amount ofcellulose aceto-propionate. I prefer to use plasticizing resins such asalkyd resins, plasticizing chlorinated diphenyls, plasticizing vinylresins, and the like.

A stripping agent may be used if desired. While not necessary for manymetal surfaces, the use of such an agent is desirable, particularly witheasily wetted metal such as unpolished steel. Typical stripping agentsare the citrate of the mono-ethyl ether of diethylene glycol (Carbitolcitrate) and Alumileaf (a proprietary product sold for improving theleafing of aluminum paint). When used, they are ordinarily present inamounts varying from a few (about three) tenths of a percent to a few(about three) percent of the composition.

A most important consideration in my new compositions stems from mydiscovery of the fact that a stripping lacquer, in order to besatisfactory, must deposit a film of at least about 1 mil in drythickness; thinner films do not strip properly, no matter how strong thefilm is. This hecessity for a thick film in one coat requires highsolids in the lacquer. High solids are ordinarily attained by the use ofa low viscosity cellulose derivative combined with large quantities ofplasticizer or resin. Such normal high solids lacquers are, however, notuseable as stripping lacquers because of their formulation, beinggenerally too adherent, as well as either soft (too much plasticizer) orbrittle (too much resin) for proper stripping.

Hence, I produce high solids by the use 01 so]- vents, oi. which atleast 75% are active solvents for the cellulose aceto-propionate. Thesesolvents not only produce a thinner solution at a given solids content,but they have two other eiIects-they insure maximum film strength byeliminating any blushing tendency, and they permit spraying atrelatively high viscosity, thus permitting the use of higher solidsagain. I have found that my compositions. in order to produce films orat least about 1 mil in thickness, should have a minimum viscosity of 50seconds in a No. 4 Ford cup at 70 F. Spraying lacquers may go up toabout 100 seconds in viscosity; above that, very poor spraying results.Brushing lacquers may be as high as 200 seconds in viscosity. Theseviscosities compare with the approximately 20 second viscositiespreferred in ordinary spraying lacquers.

Typical examples of my invention are the following:

Ezample 1 Parts by weight Hercose AP low viscosity (cellulose acetopropionate low viscosity-15.5% acetyl,

31.5% propionyl content) 7.35 Alkyd resin 7.35 Ethyl acetate 35.30 Butylacetate 45.00 Cellosolve acetate hydroxyethyl acetate--- 5.00

The alkyd resin is prepared by reacting Parts by weight Sebaci: acid37.5 Succinic anhydride 28.6 Ethylene glycol 19.3 Glycerol 14.6

Example 2 Parts by weight Tricresyl phosphate 5.65 #1254 Aroclor(chlorinated diphenyl 54% chlorine) 2.80 Carbitol citrate 2.00 Ethylacetate 40.00 Butyl acetate 34.45 Hercose AP low viscosity 8.90 VinyliteA. Y. A. F. (low viscosity polyvinyl acetate) Cellosolve acetate 5.30

This product diil'ers from that 01' Example 1 in containing carbitolcitrate, a stripping agent.

Example 3 The product of Example 2 may be colored by the use of dyesolutions (e. g. alcohol soluble dyes in alcohol) or by the use of avery small amount of pigment (e. g. 0.1% of phthaloeyanine blue orgreen).

Example 4 Paste: Parts by weight Zinc chromate 57.49 Tricresyl phosphate42.06

Grind two runs on a three-roll mill.

Parts by weight Paste 5.40 #1248 Aroclor (chlorinated diphenyl- 48%chlorine) 6.00 Ethyl acetate 33.23 Butyl acetate 33.93 Cellosolveacetate 5.07

Hercose AP low viscosity (cellulose aceto- This product is low inplasticize and high in cellulose derivative-it has unusually hightensile strength.

The small amount of pigment shown in Example 3 has little effect on thefilm: however. the 3% of pigment in Example 4 improves the ability ofthe film to withstand drawing and forming. Where it is desired to getsuch an improvement in properties, I may add a small amount (1 to 5%) ofinert extender pigment, with or without a smaller amount of colorpigment. This produces a film which can be marked with a pencil, etc.for lay-out purposes. A typical example is the following:

Example 0 Parts by weight Santocel (silica aerogel) 10.01 Surfex(calcium carbonate) 2.88 Hercose AP low viscosity (cellulose acetopropionate low viscosity-15.5% acetyl,

31.5% propionyl content) 4.47 Alkyd resin of Example 1 -i. 4.47 Ethylacetate 32.34 Butyl acetate 41.20 Cellosolve acetate 4.03

100.00 are ground in a mill to a smooth paste.

Parts by weight Above paste 15.00 -Hercose AP low viscosity (celluloseaceto propionate low viscosity-15.5% acetyl,

31.5% propionyl content) 6.25 A kyd resin 01 Example 1- 6.25 Ethylacetate 29.75 Butyl acetate 38.25 Cellosolve acetate 4.25 Chrome greenpigment paste .25

Other extenders which can be used include various clays, magnesiumsilicate, barytes in various i'orms, calcium sulphate in various forms,diatomaceous earths, and similar inerts.

The examples can be multiplied indefinitely without departing from thescope of the invention, which is defined in the claim.

Cellulose aceto-propionate of approximately 15.5% acetyl and 31.5%propionyl content Alkyd resinand a solvent fo such binder comprising thefollowing ingredients in parts by weight:

Butyl acetate 45.0t Ethyl acetate 35.30 Hydroxyethyl acetate 5.00

said allgvd resin being prepared by reacting the iollowing ingredientsin parts by weight:

Patent No. 2,421,001.

6 Sebaclc acid 37.5 Succinlc anhydride 28.6 Ethylene glycol 19.3Glycerol 14.6

HARRY K. ASH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,186,454 Gloor Jan. 9. 19402,170,416 Klinger Aug. 22, 1939 1,934,824 Schwalbe Nov. 14, 1933 FOREIGNPATENTS Number Country Date 736,429 France Sept. 19. 1932 OTHERREFERENCES Gloor, pages 690-898, Ind. and Eng. Chem., June 1937.

Certificate of Correction May 27, 1947.

HARRY K. ASH

It is hereby certified that errors appear in the printed specificationof t t re uirin correction as follows: numbered pa en q g 57.49 read57.94; and that the said Letters read Carb'itol; line 72, Example 4, for

the above Column 3, line 62, for carbitol Patent should be read withthese corrections therein that the same may conform to the record of thecase in the Patent Office.

Signed and sealed this 5th day of August; A. D. 1947.

LESLIE FRAZER,

First Assistant Commissioner of Patents.

Cellulose aceto-propionate of approximately 15.5% acetyl and 31.5%propionyl content Alkyd resinand a solvent fo such binder comprising thefollowing ingredients in parts by weight:

Butyl acetate 45.0t Ethyl acetate 35.30 Hydroxyethyl acetate 5.00

said allgvd resin being prepared by reacting the iollowing ingredientsin parts by weight:

Patent No. 2,421,001.

6 Sebaclc acid 37.5 Succinlc anhydride 28.6 Ethylene glycol 19.3Glycerol 14.6

HARRY K. ASH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,186,454 Gloor Jan. 9. 19402,170,416 Klinger Aug. 22, 1939 1,934,824 Schwalbe Nov. 14, 1933 FOREIGNPATENTS Number Country Date 736,429 France Sept. 19. 1932 OTHERREFERENCES Gloor, pages 690-898, Ind. and Eng. Chem., June 1937.

Certificate of Correction May 27, 1947.

HARRY K. ASH

It is hereby certified that errors appear in the printed specificationof t t re uirin correction as follows: numbered pa en q g 57.49 read57.94; and that the said Letters read Carb'itol; line 72, Example 4, for

the above Column 3, line 62, for carbitol Patent should be read withthese corrections therein that the same may conform to the record of thecase in the Patent Office.

Signed and sealed this 5th day of August; A. D. 1947.

LESLIE FRAZER,

First Assistant Commissioner of Patents.

